1. Field of the Invention
The present invention relates to processes and computer systems realizing redundant arrays of inexpensive disks using an on-board small computer system interface, and, more particularly, to computer processes and systems providing the capabilities of redundant arrays of inexpensive disks by using an on-board SCSI controller, and a RAID card that is not equipped with a SCSI controller mounted in an option card slot.
2. Description of the Related Art
Among the many developments computers have undergone over the years, that of increased memory is indisputably one of the most significant. Accordingly, with the vast amount of data that desktop, laptop and notebook type personal computers (e.g., "PCs") can now store and process, reliability of memory has become of utmost importance. Where multiple hard disk drives (i.e., "HDDs") are used to provide the personal computer with a high level of operational and permanent memory, the reliability of the system is in fact reduced, and problems in the management of the hard disk drive, as well as in the writing of data into and the reading of data from the hard disk drive may occur. Reliability can be especially problematic with systems used for applications that require long running times such as computer systems employed in banks, research centers, financial offices, police stations, and other data intensive applications. These problems have received the attention of the industry, generally with efforts to expand the capacity of the computer system, often with adapter and daughter cards such as the Computer System Modular Add-In Daughter Card For An Adapter Card Which Also Functions As An Independent Add-In Card, U.S. Pat. No. 5,611,057, and the Computer System SCSI Adapter Card Including An Add-in Daughter Board Providing An External SCSI ConnectorForModularAnd Upgradable SCSI Bus Routing Options, U.S. Pat. No. 5,628,637, of V. Pecone, et al. Other efforts are represented by the SCSI Connector And Y Cable Configuration Which Selectively Provides Single Or Dual SCSI Channels On A Single Standard SCSI Connector, U.S. Pat. No. 5,745,795 of V. Pecone, et al., the Add-in Board With Programmable Configuration Registers For Use In PCIBus Computers, U.S. Pat. No. 5,737,524 of A. Cohen, et al., and the Host Adapter Providing Automatic Terminator Configuration, U.S. Pat. No. 5,680,555 of M. J. Bode, fail to recognize the problems attendant to the use of multiple hard disk drives. More recent efforts include the Computer System Having A Virtual Drive Array Controller, U.S. Pat. No. 5,809,285 of Jeffrey R. Hilland, have suggested a computer system with a front end coupled to a secondary storage bus and a back end coupled to a plurality of physical memory devices.
Redundant arrays of inexpensive disks (i.e., "RAID") technology have endeavored to address these problems of reliability. Although RAID technology was originally designed to enhance the performance ofthe input and output (i. e., "I/O") subsystem of personal computers, as this technology progressed it became clear that the main advantages of a RAID system lay in data availability and reliability rather than in performance enhancement. RAID was originally defined by Patterson, Gibson and Kats in a paper entitled A Case for Redundant Arrays of inexpensive Disks published by the University of California at Berkeley, during 1987. This paper defined five RAID levels ranging from Level One through Level Five. Subsequently, the personal computer industry has added a sixth level called level Zero, that provides no redundancy features but stripes data across the disks. Five of these six levels, namely levels Zero, One, Three, Four and Five feature prominently in the commercial world. The appropriate RAID level is selected to satisfy the input and output stage requirement of the user.
As customarily implemented, RAID uses a plurality of low-cost disk drives to form an array, and offers substantial performance improvements over the alternative of a single large expensive drive (i.e., "SLED") technology. The mean time between failure is the same as when one disk drive is used because the computer recognizes the array of disks as a single drive. Moreover, RAID is a fault tolerant solution based on software that enables variances in structure according to the intent of the manufacturer and the requirements of the user's computer system. Furthermore, the design of each array controller can be made differently to obtain data availability targets and specific applications.
A hot swap is a technique for replacing (e.g., as by swapping) either the hard disk drive or another auxiliary storage device, by using a single connector attachment (i.e., a "SCA") without turning off the application of electrical power to the computer. With this capability, a RAID can recover during failure of a hard disk drive and data can be automatically recovered without first turning the computer off.
Although redundant arrays of inexpensive disks were formerly used solely in mainframe computers and servers, redundant arrays of inexpensive disks are being increasingly used in personal computers because RAID systems advantageously enable a computer system to be used continuously even when the hard disk drive suddenly malfunctions, and because RAID systems permit an easy replacement of the faulty hard disk drive.
Conventionally, a redundant array of inexpensive disks requires a RAID card that typically bears a SCSI controller, end is mounted on a motherboard. The typical motherboard has an on-board SCSI controller and a SCSI connector, that are mounted on the computer's motherboard. The RAID expansion card must bear in addition to its SCSI controller, a PCI interface controller and a RAID controller, I have found that the overall price of the RAID card is unnecessarily high, that the configuration ofthe circuit for the computer system is exceptionally complex and difficult to design, and that it is increasingly difficult to manufacture the computer system to conform to industry wide standards such as PCI and EISA.